1. Field of the Invention
The instant invention relates to communication systems, and more particularly, the instant invention relates to systems for generating codes in a communication system such as security system wherein the codes are identified with specific transmitters.
2. Technical Considerations and Prior Art
Existing state of the art security systems which monitor a plurality of locations are generally very expensive to install and require expensive computerized equipment to operate. Moreover, existing systems are not easily adaptable for individual use wherein a single person carries a transmitter with him which can instantly notify a central monitoring station as to the identity and location of that individual should the individual encounter trouble. Existing systems may indicate that an individual may be experiencing difficulty, however, the identity and location of the person experiencing difficulty cannot be determined precisely utilizing existing systems.
A relatively simple system has been developed for use with garage door-openings. U.S. Pat. No. 4,178,549 and U.S. Pat. No. Re. 29,529 disclose such arrangements. However in each case, there is a single receiver which responds to only one pulse-width modulated code rather than responding to a plurality of different pulse-width modulated codes. In other words, the received signals are matched instead of being read. The particular technology utilized in these patents does not require expensive computerized equipment and is widely used by consumers. Even though such a system is very difficult to jam or deceive, yet it has not been utilized for alarm systems. There are of course numerous disclosures of a single receiving station which responds to a plurality of separate stations or conditions. Patents indictative of this arrangement are U.S. Pat. Nos. 3,209,342; 3,299,404; 3,289,107; and 4,047,107. However, none of these references disclose a passive receiver which simply reads pulse-width modulated signals. The prior art does not suggest that enormous savings in costs while an increase in capacity of a communications system exemplified by a security system may be effected by utilizing pulse-width modulations as suggested in U.S. Pat. No. 4,178,549 and U.S. Pat. No. Re. 29,529.